KSM, as Mohammed is known throughout the American intelligence apparatus, has admitted to planning and managing the attacks from “A to Z,” as he described it. It was but one of dozens of attacks in which he played a role, often the major one.

Yet what little most Americans know about KSM is what they have gleaned from that famous photo of him in his nightshirt. Who is Khalid Sheikh Mohammed?

Mohammed is a Pakistani national, a member of the Baluch tribe predominant in the border regions where Pakistan, Iran, and Afghanistan meet. His father, an imam, was recruited to lead a mosque in Kuwait during the early oil-boom years and Mohammed was born there in 1965, the youngest of a large family. His father died when he was young and his much older brothers, in particular the oldest, Zahed, helped raise him. He followed Zahed’s example and as a teenager became active in the Muslim Brotherhood, which in those years preached an especially virulent anti-Semitism.

The brothers sent Khalid to the United States to attend college and he earned a mechanical-engineering degree from North Carolina A&T. After graduation, he complained that Americans hated Muslims and loved Jews.

Unable to find work in Kuwait when he returned there after college, he joined his three brothers who had gone to support the American-funded, anti-Soviet jihad in Afghanistan. In a lot of ways, this was a life a similar to those lived by many of his contemporaries. He was a striver, upwardly mobile (earning a graduate degree by correspondence), and the glorious struggle of the jihad was the defining movement of his generation.

Then it all came crashing down. When the Soviets left Afghanistan in disgrace in 1989, the Americans withdrew as well, earning the enmity of many jihadis, including KSM. They blamed the Americans for the internecine struggle that broke out among competing Afghan political parties afterward.

The death of one of his brothers in a senseless battle not long after marked the pivotal point in his life. From the early 1990s forward, as nearly as we can tell, KSM has done nothing but conceive, plan, and execute terrorist plots. He himself has admitted responsibility in full or part for 31 separate plots. The true number is probably much larger. He conspired to kill Americans, Pakistanis, Tunisians, Indonesians, Muslims, Christians, and Jews, among many others.

He had a job as an engineer for a while and explored some business deals—exporting palm oil, importing frozen chicken parts—but these were always in service of his larger terrorism endeavors.

His record is startling in its extent, shocking in its ferocity. There was a casual, almost feral quality to his plotting. Some attacks, 9/11 being the most notable, were years in the planning, carefully tended through to execution. Others were seemingly spur of the moment. Shorting after meeting him, for example, he persuaded a young Pakistani American to take part in a suicide bombing at his own wedding. He pitched plots like a door-to-door salesman hawking pots and pans.

It’s in this incarnation as a sort of Johnny Appleseed of terror that Mohammed’s character is most plainly in view. Unlike Osama bin Laden, who always seemed an aloof, distant presence, KSM thrived down in the muck of the everyday world. He was a family man who played with his children and loved Iranian dates. He argued over hotel bills and bragged to associates of his importance.

Mohammed was an adept and relentless networker with a gift for small talk and instant familiarity. A friend recalls running into him once on a street outside a mosque in Qatar. While they talked, a constant stream of people kept coming up to Mohammed to say hello, shake his hand, exchange warm good wishes. Mohammed seemed to know them all and had a kind word, or maybe a joke, for each. He couldn’t have been more charming.

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He was physically unimpressive—short, stout, bespectacled. He used this charm cold-bloodedly to recruit young men into his plots. He shared with his nephew, Ramzi Yousef, the man who bombed the World Trade Center the first time, a rough, happy-go-lucky charisma that they used to persuade others to go along with what must often have seemed outlandish schemes. They were hustlers, raconteurs, and had an affability about them that suggested they would make excellent dinner companions. They flirted with women and joked with men. They brought this same casual air to their plots, a kind of off-the-cuff, what-the-hell approach, as if blowing up buildings full of people were a perfectly normal thing to do.

They were multilingual, fluent in Arabic, Urdu, Baluch, and English, and moved easily through a globalizing world. They changed identities as one might change shoes. They picked targets to suit the moment.

Mohammed’s relentlessness is best revealed not in the September 11 plot but in everything that followed.

The U.S. military response to the 9/11 attacks was launched on October 7, 2001. It was swift and devastating, unseating the Taliban government in Afghanistan by Thanksgiving. Al Qaeda, without a sponsor, was dislodged and on the run. When the United States declined to deploy enough troops to block their exit, bin Laden and Ayman al-Zawahiri escaped through the snowy passes of Tora Bora into Pakistan. Others weren’t so lucky. Mohammed Atef, the military commander of al Qaeda, was killed in Kandahar—under bombardment from American air forces—in mid-November. Atef had been among bin Laden’s most influential aides, and his death left a huge void in al Qaeda’s leadership. Khalid Sheikh Mohammed filled it.

Mohammed took charge of bringing some order to the retreat from Afghanistan. He convened a meeting of al Qaeda leadership in December in Zormat, in eastern Afghanistan. Before the attacks, KSM had helped organize a collection of safe houses in Karachi and elsewhere in Pakistan, many of them operated by sympathetic jihadi groups like Lashkar-e-Taiba, with whom KSM had had a relationship for years.

KSM had been living in Karachi off and on since 1992 and had developed connections throughout this underground, immersing himself in the jihadi world of Pakistan and cultivating relationships among its many branches. It is almost impossible to overstate the importance of such groups throughout Pakistan. Within Pakistan’s urban areas, they are nearly omnipresent, and in some cities they control entire districts. After the 9/11 attacks, the groups were indispensable in helping KSM evacuate key operational al Qaeda members from Afghanistan into Pakistan and helping them regroup, in part by providing money, logistics, safe havens, and a ready army of trustworthy foot soldiers.

Those connections and his ties with a network of ethnic Baluch, including his family, formed the basis of KSM’s ability to operate throughout the country. KSM’s extended family provided a haven to which he retreated when the need arose.

Much of al Qaeda’s membership seemed panicked by the ferocity of the American response to September 11. Initially, KSM was concerned, too. He later told a U.S. interrogator that he rejoiced until the moment the towers fell down. “Shit,” he said. “We’ve awakened a sleeping bear.... I think we bit off more than we could chew. We had no idea what the cowboy [Bush] would do.”

It didn’t take KSM long to recover his swagger. In some ways, it was as if he had lived his whole life to prepare for this moment. He arranged passage and shelter for terrorists who would scatter across the Subcontinent, and often helped them through to the Middle East, Africa, Southeast Asia, and the Americas, where they were able to reform al Qaeda cells and launch attacks. The exodus was accomplished while the eyes of the world were trained on the region, looking for exactly this sort of activity.

KSM seemed not to notice. He traveled freely, commuting to the Afghanistan borderlands over and over in the months immediately after 9/11. He detailed plans and directives. He dispensed cash by the hundreds of thousands of dollars. He calmed jittery nerves and organized training classes, giving al Qaeda refugees something to do while they awaited transit. The instruction was hardly innocuous. KSM wanted his fighters to be trained in assassinations and kidnappings so that they could mount such operations against Americans when they returned to their home countries.

He focused his charm particularly on young men with Western passports or other connections that would make transit simpler and safer. Using men already at home in the West eliminated much of the difficulty of crossing international borders.

KSM sent Mohammed Jabarah, a Kuwaiti-born Canadian citizen, to Singapore to study attacks against Western embassies there. He sent Jack Roche, a British-born citizen of Australia, to Australia to bomb government buildings there; he worked closely with Christian Ganczarski, a German national, to attack a synagogue in Tunisia. Adnan el-Shukrijumah, a Saudi-born Florida resident, and Dhiren Barot, a British citizen of Indian descent, were tasked with casing potential U.S. targets, including Wall Street and the Panama Canal.

What was extraordinary about KSM’s plans, apart from the sheer volume of them at a time when he could have been laying low, was the degree of personal attention he devoted to the recruits he designated to execute them. He was able, somehow, to shield them from the biggest counterterrorism dragnet in history—and not just in Pakistan but in those other countries to which he had sent operatives and support cells. Unlike the 9/11 plot, in which he used intermediaries, or cutouts, to disburse funds and communicate with the pilots and hijackers, he personally directed many of these smaller plots. Jabarah spent an entire week in KSM’s Karachi apartment before being sent to Southeast Asia. KSM shepherded Roche back and forth between safe houses in KSM’s traditional mode of travel: a Karachi taxi with a personal driver.

He usually introduced himself as Mukhtar, and in at least one instance asked that he be addressed in email communications as Mukh. He so endeared himself to a young Pakistani American, Majid Khan, that Khan referred to him familiarly as Chacha—“Uncle” in Urdu.

KSM also didn’t mind boasting a bit —“big-noting himself,” as Roche put it. KSM told Roche he controlled all the al Qaeda cash that came through Pakistan, saying that at one point he had received a suitcase stuffed with $400,000.

He oversaw specially trained groups of document forgers and travel facilitators who churned out the documents needed to stay safely in Pakistan, or to travel through so they could help rebuild the network elsewhere. He went about his main business much as he had before. This meant mainly one thing—more plots.